The present invention relates to a screen which can be used in a digitizer and to a method of making such a screen. More particularly, the invention relates to a screen which includes a sheet of conductive plastic material which is perforated and may be laminated to a sheet of rigid material, such as glass.
Digitizing devices which are capable of translating the positioning and movement of a stylus or other element on a screen into electrical signals representative of such positioning and movement are well known. One such device is the subject of U.S. Pat. No. 4,665,283, entitled "Electrographic Apparatus", inventors Robert G. Kable and Philip A. Schlosser, issued May 12, 1987. This patent shows a digitizer screen in which a resistive surface or sheet which may be formed of a layer of indium-tin-oxide is deposited onto a dielectric support material such as glass. Voids or discontinuities are formed in the resistive layer to increase the edge-to-edge resistances of the layer and to provide identical edge-to-edge resistances in the x- and y- coordinate directions for digitizers which are rectangular and non-square. The conductive coating on the glass is applied in a waffle-like pattern. Among the purposes served are the following. The decreased active area of the resistive layer minimizes electrical noise which might be introduced by capacitive coupling with the user's hand as it rests on the screen. The patterning allows the effective load of the digitizer screen to be optimized for both the drive electronics and the transparent conductive coating manufacturing process. Transparent conductive coatings, such as the indium tin oxide coating described in the patent, achieve lowest cost, optimal uniformity, and highest durability only at low sheet resistances (somewhere on the order of 200 ohms/square) due to manufacturing limitations. The circuitry used to drive the digitizer screen, however, works best at higher sheet resistances. The patterning effectively increases the overall sheet resistance, thus allowing a compromise between the two. By making the squares of the waffle pattern rectangular instead of square, the effective load presented to the drive electronics can be made the same in both the x- and y- directions. Otherwise, due to the different characteristics in the two directions, one direction would be more susceptible to noise pickup than the other. Also, overall light transmission is improved by the patterning. The conductive coating tends to block light and create glare.
An improved film or coating which is used in association with the glass or other rigid element, and which results in lower cost and increased durability, would be advantageous.